The present invention relates to a method for manufacturing non-oriented silicon steel sheet and strip having a smooth surface condition without the defect of ridging. Particularly, it relates to a method for manufacturing non-oriented silicon steel sheet and strip having no ridging, in which molten silicon steel, whose composition is controlled properly, is made into a slab by casting, and said slab is dealt with by a combination treatment comprising hot-rolling, cold-rolling and annealing.
In recent years, the technical development in the manufacture of non-oriented electrical steel sheet and strip has been very remarkable.
Particularly, various newly developed technics such as, controlling the composition of the molten steel, for instance, by vacuum degas treatment, and ingot making of molten steel have been introduced in the manufacture of electrical steel sheet and strip, and consequently excellent electrical steel sheet and strip can be manufactured.
However, as a result of introducing such new techniques, while a remarkable effect can be obtained on one hand, new defects are occuring on the other hand.
As an example, particularly, in manufacturing high quality non-oriented electrical steel sheet and strip, when a cold-rolled non-oriented steel strip is manufactured by a combination treatment, comprising a degassing treatment under reduced pressure, continuous casting and cold-rolling, lengthwise strips called ridging appear continuously in parallel with the rolling direction on the surface thereof.
The above-mentioned lengthwise stripes, namely, ridging or ribbing or roping, demonstrate continuous undulation in the form of so-called lengthwise stripes along the rolling direction on the surface of the cold-rolled steel sheet, wherein the crest and the trough of the foregoing undulation are extended to run nearly in parallel with the rolling direction. As one surface of the produced steel sheet is being formed, for instance, in a concave shape, the other surface thereof which corresponds to said one surface would be formed naturally in a convex shape, the configuration of the upper surface and the lower surface of the steel sheet should be closely matched with each other. Further, the undulation on the surface of the steel sheet is adapted to be increased as the increase of the frequency of the working processes for the steel sheet.
The present invention will be explained referring to the attached drawings.